Cyclohexanedimethanols are important intermediates for producing a variety of polyesters for coatings, fibers, molding plastics, packaging materials, and the like. Cyclohexanedimethanols are typically manufactured by the hydrogenation of the corresponding cyclohexanedicarboxylate esters. For example, one of the more commercially important cyclohexanedimethanols, 1,4-cyclohexanedimethanol (abbreviated herein as “CHDM”), typically is prepared by a two-step hydrogenation process involving hydrogenation of dimethyl terephthalate (abbreviated herein as “DMT”), to give dimethyl 1,4-cyclohexanedicarboxylate (abbreviated herein as “DMCD”), followed by hydrogenation of the ester groups. The various steps of this process have been described, for example, in U.S. Pat. Nos. 3,334,149, 6,919,489; 5,399,742; 5,387,752; 5,395,987; 5,185,476; and 7,632,962; and United Kingdom Patent Application No. 988,316.
The use of DMT as starting material for the preparation of CHDM presents several challenges. DMT is typically prepared by the esterification of terephthalic acid with methanol under high pressures and temperatures that requires expensive, specialized process equipment and can result in increased energy consumption and operating costs. Further, during the esterification process, DMT tends to form solids within the reflux zones of the process, which can cause plugging and reduce the efficiency of the heat exchange surfaces. Other solvents such as, for example, xylene may be introduced in the reflux zone to help liquify the DMT, but this solution places additional purification requirements on the DMT process. DMT must also be distilled prior to its introduction into the hydrogenation step of the CHDM process in order to remove partial esterification products and any esterification catalysts that can poison and/or reduce the activity of the downstream hydrogenation catalysts. Finally, the hydrogenation of DMT releases methanol that requires additional purification and processing steps in order to recover and recycle the methanol from the CHDM hydrogenation product mixtures. The use of alternative CHDM feedstocks that avoid these difficulties, therefore, could greatly improve the efficiency and reduce the equipment and processing costs of the CHDM process.